1. Field of the Invention
This invention relates to a cushioning device for absorbing shock between railway cars, and in particular, to a cushioning unit having a detection device for indicating failure of the cushioning unit.
2. Description of the Prior Art
Railcars experience a great deal of shock during coupling operations and other train action. This shock can damage cargo on the railcars and the railcars themselves. To absorb the high forces experienced by railcars during these operations, cushioning devices have been employed between the frame of the railcar and its couplers. These shock absorbers absorb shock energy induced when the car is pushed into other cars during coupling operations. Shock energy is also absorbed during "over-the-rail" operations when adjacent coupled cars develop relative motion with respect to the adjacent freight car.
The shock experienced by railcars results from both buff and draft forces applied to the coupler of the railcar. The term "buff" is used to describe the movement experienced by a coupler when it is moved toward its associated railcar. These buff forces are usually experienced during coupling operations between the railcars. "Draft" describes the outward movement of the coupler away from its associated railcar in response to pulling forces acting on the coupler.
The shock absorber is commonly referred to as a cushioning unit and is comprised of a hydraulic cylinder and a piston. The cylinders are filled with a hydraulic fluid which is forced through small diameter ports in the cylinder wall in response to impact force applied to the piston. Spring means and sometimes pressurized gas are used to supply a restoring force for the cushioning unit. Difficulty has been encountered in the past in testing these cushioning units once they are installed on the railcar. Prior methods of testing these cushioning units involve pushing the cars with a locomotive into an adjacent car to see how fast the cushioning unit responds. Depending upon how fast the cushioning unit responds, an observer can determine if the cushioning unit is defective. Failure of the cushioning unit can often be attributed to a broken piston shaft, a broken piston or loss of hydraulic fluid.
In gas restored cushioning units, another method of determining whether the cushioning unit is defective is to provide a pop-up type pressure valve which responds to a preselected low pressure within the cylinder. When the pressure within the cylinder drops below this preselected level a stem of the pressure valve pops in to indicate that the cushioning unit has lost restoring gas pressure. While this method determines lost gas pressure, it does not activate for most normal failure modes. The pop-up valve may also indicate a defective unit even though the cushioning unit is properly restoring.
This indirect approach of determining failure of the cushioning unit does have disadvantages. Because the use of a pressure valve only gives an indication that the pressure within the hydraulic cylinder is below a preselected level, the failure of a cushioning unit due to broken piston head, broken piston shaft or other common problem would not necessarily be indicated using the pressure valve.
What is therefore needed is a detection device or a method of detecting failure of a cushioning unit on a railcar which can be used without having to actuate the cushioning unit itself other than observing or inspecting the detection device. The need also exists to be able to isolate the unit being tested from units on other railcars and the type of activity causing the cushioning unit movement.